The study is designed to examine the relative contribution of sinoaorter baroreceptors in controlling changes in renal function during alterations in effective blood volume. Studies will be conducted in a control group of dogs and in a group of dogs with selectively denervated sinoaortic baroreceptors. The experiments will determine if the reflex antidiuresis associated with the application of positive end expiratory pressure breathing and the reflex diuresis of atrial tachycardia are initiated by sinoaortic baroreceptors. Also, the role of sinoaortic baroreceptors and cardiopulmonary receptors in influencing renal function in response to a hemorrhage will be examined.